Liquid Hold-up Volume and Phase Ratio (A/O) of HNO3–DtBuCH18C6/n-Octanol System in an Annular Centrifugal Extractor

ABSTRACT The crown ether strontium extraction (CESE) process has been developed for the recovery or removal of Sr from acidic high-level liquid waste (HLLW) in China, where the extractant is 4’,4”(5”)-di-(tert-butyldicyclohexano)-18-crown-6 (DtBuCH18C6) and the diluent is n-octanol. When the CESE process was operated in annular centrifugal extractors (ACEs) for demonstration by cold and hot tests, it was found that the outlet aqueous phases had organic-phase entrainment even though ACEs operated at a low rotor speed. For the successful operation of the CESE process in ACEs, effects of the operating and geometrical parameters on the liquid hold-up volume and phase ratio (aqueous phase/organic phase, A/O) of the HNO3 –DtBuCH18C6/n-octanol system in a ϕ20 ACE were systematically investigated to find the cause of the above-mentioned hydrodynamic performance problem of the CESE process using the liquid-fast-separation method. It is shown that the operating and geometrical parameters have effects on the liquid hold-up volume and phase ratio (A/O). Moreover, the phase ratio (A/O) in the separation zone of the rotor is less than 1.5 under most of the present experimental conditions, which shows organic-phase entrainment may easily occur in the outlet aqueous phase. The cause can be that the density difference of two phases is small, viscosity of the organic phase is large, and interfacial tension of the extraction system is low.